It has now been recognized that the world's environment is suffering too much from global warming caused by greenhouse gas exposure in the atmosphere. To address this problem governments are now starting to adopt targets for reducing the emission of greenhouse gases to the environment and play their part to address this problem for future generations. While some countries have not adopted a firm goal, other countries, for example Australia, have adopted a policy for the reducing greenhouse gases by 20% by the year 2020.
Greenhouse gases can be emitted from cars, industry, farming, and households to name a few. While certainly not as apparent as a large factory with tall smokestacks, within a normal household the gas burning appliances, such as furnaces, water heaters, etc., all release such greenhouse gases as a by-product of the combustion process itself. While the appliance industry has taken a leading role in energy efficiency and environmental concern, further improvement is always foremost in mind of the appliance design engineer.
With such further improvement in mind, especially with the increased awareness of global climate change and changing governmental regulations, it is noted that hot water heaters, both internal and externally installed units, can be one of the more fairly inefficient appliances in energy conservation, and therefore require the burning of additional fuel to maintain the set point temperature. This, of course, results in the additional production of greenhouse gas beyond that which a more efficient appliance would produce.
A typical hot water heater includes a vertical tank with a centrally located flue pipe. A gas burner is positioned underneath the tank and is controlled by a combination gas controller valve. The combination gas controller valve incorporates an On/Off valve, a pilot safety circuit, pilot and main burner pressure regulators and their associated supply pipe connections, as well as a thermostat to control the hot water heater to maintain the water in the storage tank at a predetermined temperature.
Upon the thermostat calling for more heat, the main gas valve opens to allow gaseous fuel (gas) to flow to the main burner where it is ignited by the pilot light. Ignition and combustion of the gas results in hot flue gas being generated. The heat from the hot flue gases is transferred to the cold water via the bottom of the tank and through the walls of the central flue pipe. The flue gases exit out the top of the hot water heater.
There are generally two types of hot water heaters used throughout the world classified by their installation location. For an indoor water heater such as used in the North American market, the hot flue gases exit through a draft diverter that is connected to a flue pipe which pipes the flue gases safety to an outside location. Air for combustion of the gas is drawn into the combustion chamber at the bottom of the hot water heater. For an outdoor hot water heater such as used in the Australian market, the flue gases pass safely through a balanced flue terminal at the top of the heater to the outside atmosphere. The balanced flue terminal is so designed to allow a continuous supply of air for combustion irrespective whether the burner is on or off under all types of wind conditions. The air for combustion is transferred to the bottom of the heater internally within the appliance.
For each of these two types of hot water heaters, many manufacturers are offering configurations that are flammable vapor resistant. Flammable vapor resistant hot water heaters normally have a flame trap in the bottom of the combustion chamber as the fresh air inlet. The flame trap is a special design to allow air for normal combustion and also any flammable vapors to enter the combustion chamber. Such flammable vapors may be the result of an accidental gasoline spill, for example. The design is such that any resultant ignition/explosion due to flammable vapors (e.g. gasoline) in the combustion chamber will not escape the appliance and ignite the spill outside the appliance. Such designs have recently been mandated in the United States.
As a result of the two requirements, i.e. ensuring ignition of the main burner upon a call for heat and safely igniting any flammable vapor that enters the air intake, the positioning of the pilot and the size of the pilot flame itself become very important.
Unfortunately, one of the current disadvantages for hot water heaters is the overall service efficiency of the appliances. Service efficiency is defined as the energy delivered to the hot water from the hot water heater each day, divided by the energy burnt in the gas to heat the water and to maintain the hot water in the tank at the desired temperature. The service efficiency may vary from around 0.50 or 50% for poor performing appliances, to appliances just complying to US regulations around 0.59, to superior products from 0.64 or 64% service efficiency. Low service efficiency may be due to poor thermal efficiency of the heat into the water when the burner is on and/or excessive heat losses when the burner is off. Since the main burner is only on for one to two hours per day heating the stored water to keep it ready for use, burning of gas for the pilot for the remaining 22 hours only contributes to the inefficiency issues.
As is clear from the foregoing, there is a need in the art for a pilot control system for a hot water heater that conserves energy and yet still ensures ignition of the main burner and safe ignition of flammable vapor. Embodiments of the present invention provides such a pilot control system. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.